The popularity of coffee and espresso drinks has grown recently, and in-home espresso machines are becoming more and more commonplace. These drinks conventionally have been prepared by brewing, where hot water passes through coffee grounds above a filter, under pressure in the case of espresso machines. Indeed, a defining characteristic of electrical espresso machines is that the coffee grinds are infused with hot water under a substantially constant high pressure supplied by an electrical pump. The hot water pressure is usually more than 100 psi throughout the infusion/extraction cycle.
Conventional electrical espresso machines contain the following major components in sequence: a cold water reservoir or direct connection to external cold water supply; a cold water pump; a boiler or thermo-block; a group/brew head; and a portafilter. These components are usually arranged in side-by-side relation. The machines operate as follows. The boiler is filled with water and preheated to a temperature greater than 180° F. prior to activating the pump. During the brewing process, the pump pressurizes the cold water from the water reservoir and injects it into the hot boiler. The pressure from the incoming water forces the hot water already in the boiler into the group or brew head. The hot water than infuses the coffee in the portafilter, and exits into a cup or other receptacle placed under the portafilter.
Typically, espresso machines for home use are larger than about 14 inches high, 10 inches long and 8 inches deep, weigh more than twenty pounds, and require more than 1 kW power to operate. The minimum size and weight of known espresso machines are in part limited by the process sequence described above. For instance, the water is completely unheated before entering the pump, and is heated to the espresso temperature in a single step by the boiler or thermo-block. This requires a large volume of heated water in the boiler, and thus a powerful heater is necessary. Indeed, the water must be heated to about 205° F. in about 20 seconds, which is the optimum brewing time for espresso. Also, for temperature stability, the volume of the boiler is typically at least four times the volume of the prepared coffee, and components such as the boiler, group, and portafilter are typically made of heavy cast brass.
In view of their weight and form, known espresso machines are difficult to transport. Moreover, they cannot be used in passenger vehicles or easily packed for a trip. To be portable, an espresso machine should be lightweight, compact, devoid of protruding parts and should not occupy a large volume. They should be sufficiently sturdy to withstand rough handling. Furthermore, to be usable in a passenger vehicle, an espresso machine should have all of the above characteristics but also should require no more power than that available through a typical vehicle's power outlet, typically 120 W continuous. The machine also should be spill-proof.